1. Field of the Invention
The present invention relates to an image forming apparatus and a control method therefor, and more particularly, to an image forming apparatus such as a copying machine or a printer for performing double-sided printing and a control method therefor.
2. Description of the Related Art
Conventionally, there has been known printers for performing double-sided printing by inverting a sheet after completion of first side printing on the sheet and then performing second side printing thereon. Such printers put the inverted sheet on standby on a conveying path in the case where the second side printing on the sheet cannot be started in predetermined timing after completion of the first side printing for a reason such as delay in developing image data for image formation on the second side. Most of such printers are designed to have a conveying path which is short in length for the sake of miniaturizing, so that the sheet is partly exposed to the outside of the printer body upon inversion of the sheet (refer to Japanese Patent Laid-Open No. 05-131696 for instance).
In these printers, when the second side printing on a sheet cannot be started in predetermined timing after completion of the first side printing, the sheet is made to be on standby and the sheet put on standby is partly exposed to the outside of the printer, as described above. When the sheet put on standby is of large size such as A3 in particular, the part of the sheet exposed to the outside of the printer body is so large that a user may mistakenly pull out the sheet, judging that printing is finished.
Thus, there has been proposed a technique of canceling a printing process when a user mistakenly pulls out a sheet during printing (refer to Japanese Laid-Open Patent Publication (Kokai) No. 2001-305918, for instance).
However, the proposed prior art cannot prevent a user from pulling out a sheet during printing. Even when the user is aware of printing being in progress while pulling out the sheet from the printer and then stops pulling it out, problems are caused such that the sheet cannot be normally fed, and images are displaced relative to the sheet so that the second side printing is not normally performed.